From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin Hilman Subject: Re: [PATCH v4] i2c: davinci: Fix race when setting up for TX Date: Thu, 23 Sep 2010 07:27:38 -0700 Message-ID: <87d3s47cx1.fsf@deeprootsystems.com> References: <4C97CEC9.8060602@boundarydevices.com> <1285042408-13200-1-git-send-email-jon.povey@racelogic.co.uk> <026901cb597f$86fa9980$94efcc80$@raj@ti.com> <4C9904E6.7070608@boundarydevices.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: In-Reply-To: <4C9904E6.7070608-Q5RJGjKts06CY9SHAMCTRUEOCMrvLtNR@public.gmane.org> (Troy Kisky's message of "Tue, 21 Sep 2010 12:17:58 -0700") Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Troy Kisky Cc: Sudhakar Rajashekhara , davinci-linux-open-source-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org, linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-i2c@vger.kernel.org Troy Kisky writes: > On 9/21/2010 4:24 AM, Sudhakar Rajashekhara wrote: >> Hi, >> >> On Tue, Sep 21, 2010 at 09:43:28, Jon Povey wrote: >>> When setting up to transmit, a race exists between the ISR and >>> i2c_davinci_xfer_msg() trying to load the first byte and adjust counters. >>> This is mostly visible for transmits > 1 byte long. >>> >>> The hardware starts sending immediately that MDR.STT is set. IMR trickery >>> doesn't work because if we start sending, finish the first byte and an >>> XRDY event occurs before we load IMR to unmask it, we never get an >>> interrupt, and we timeout. >>> >>> Sudhakar Rajashekhara explains that at least OMAP-L138 requires MDR mode >>> settings before DXR for correct behaviour, so load MDR first with >>> STT cleared and later load again with STT set. >>> >>> Tested on DM355 connected to Techwell TW2836 and Wolfson WM8985 >>> >>> Signed-off-by: Jon Povey >>> CC: Sudhakar Rajashekhara >>> CC: Troy Kisky >>> --- >>> Reworked after comments by Troy and Sudhakar. >>> >>> Looking at the datasheet it seemed like setting STP without STT early >>> might cause a stray STOP to be generated, so I moved it into the second >>> MDR load. >>> >>> This passes a quick smoke test but I can't do much more testing right at >>> the moment. Sudhakar, your comments would be welcomed. >>> >> >> Looks good to me. I can test on couple of platforms I have and update the result >> by tomorrow. >> >> Thanks, >> Sudhakar >> >> >> > I like it too. I hope it works for omap. Troy, can I take this as an Acked-by from you? or a Tested-by? Thanks, Kevin